This invention relates to improved optical communication systems incorporating certain optical interleavers for de-multiplexing or multiplexing closely spaced optical channels carried by the system. This invention also relates to methods of making and using such optical systems.
There is a growing demand for increasing capacityxe2x80x94or bandwidthxe2x80x94of optical communications systems, including WAN and LAN systems. The internet has greatly increased the amount of information transmitted over optical lines used in telecommunication systems. The use of other systems, such as microwave links, coaxial cables, and copper wires is not as desirable because propagation loss can be higher and channel capacity lower, and they are susceptible to electro-magnetic interference (EMI). Optical systems have the capacity to carry optical information at rates of several megabytes per second to tens of gigabytes per second and higher. Optical system designers and operators have used higher transmission rates to push information faster along optical fibers, and have used multiplexing, including dense wavelength division multiplexing (DWDM), to increase the number of channels carried by a single optical waveguide or signal carrier. In this way, optical systems are more efficiently used. At a receiver end, channels of different wavelengths are generally separated by narrow band filters and then detected or further processed. Optical systems have been designed, for example, to divide the C-band (approximately 1,530-1,565 nm) into 40 channels with 100 GHz spacings, or even 80 channels at 50 GHz spacings. New technology and components are needed to further increase and manage bandwidth in existing and future optical systems. Interleavers are used in some systems designed to employ dense channel spacings
An interleaver, or de-interleaver used in the opposite direction, can function essentially as (or as part of) an optical router or switch or add/drop or the like, to permit a system with individual channel passband filters designed for wider channel spacing to effectively isolate individual channels having narrower channel spacings. A system with individual channel passband filters designed to operate at 100 GHz spacings, for example, can be operated at 50 GHz spacings, thereby doubling the channel count. The interleaver combines (or in the case of the de-interleaver, separates) two sets of complementary (i.e., non-overlapping) channels into a more densely packed set of channels. Stated in another way, the interleaver is capable of either multiplexing or de-multiplexing optical signals. That is, the wavelength spectrum carried by an optical system typically is divided into multiple individual channels, each capable of carrying a signal substantially of any signal carried by the other channels carried by the system. Typically, each channel is assigned or pre-allocated a narrow passband straddling a center wavelength, with substantially uniform spacing form the center wavelength of one channel to the center wavelength of the adjacent channel(s). Multiplexing and de-multiplexing the individual channels can be performed with selectively transparent filters designed to reflect all channels except the one channel to be added or dropped. Suitable passband filters are known to those skilled in the art, such as a Fabry-Perot filter comprising a single or preferably multi-cavity thin film coating deposited, e.g. by sputtering, on a surface of a suitable xe2x80x9cbulk opticxe2x80x9d i.e., a silica glass or other optically transparent substrate. As channel spacings decrease, that is, as wavelength spacing between the assigned center wavelengths of adjacent channels decrease, the difficulty and cost of producing suitable passband filters increases. Thus, while desirable increase in system capacity is achieved at higher channel counts (i.e., at closer channel spacings), there is an undesirable cost increase associated with the correspondingly more narrow passband filters. Accordingly, there is a substantial need for avoiding or reducing such passband filter cost increase.
It has been suggested to use interleavers to partially multiplex or de-multiplex channels in an optical system that employs wavelength division multiplexing. Alternating channels of a multiplexed signal, e.g., a first, third, fifth, etc. channel, are passed by the interleaver as a semi-multiplexed signal (or semi-demultiplexed signal), depending on the direction of operation), while the second, forth, sixth, etc., channels are not passed, but rather reflected back by the interleaver. In current optical telecommunications systems and other demanding optical system applications, it is now found that interleavers having improved optical performance characteristics are needed, including low insertion loss, improved passband shape, etc. Interleavers employing multi-cavity Fabry-Perot thin film coatings, as opposed to single cavity interleavers, are found to provide higher levels of optical performance. Multi-etalon interleavers, i.e., two-cavity and preferably three or higher cavity designs are believed to be necessary to provide optical performance quality and characteristics needed for many optical systems.
It has long been a recognized problem in this industry, that producing interleavers having good optical performance characteristics can be difficult and expensive. In addition, there are industry-recognized problems associated with producing structurally robust interleavers comprising etalons having desired, precise optical properties. Prior known interleavers have employed etalons of various designs, such as the etalons used in the interferometric optical devices of U.S. Pat. No. 6,125,220 to Copner et al. In the interleaver/de-interleaver devices of Copner et al, two glass interferometric end plates are separated by a spacer region where the etalon is formed. The spacer region is an air gap having a predetermined dimension. In adjustable Fabry-Perot devices, such as those disclosed in U.S. Pat. No. 5,283,845 to Ip, tuning of the center wavelength of the spectral passband of an etalon is achieved by varying the effective cavity length (spacing) between two end plates carrying thin film reflectors. More specifically, in Ip a piezo actuator is used, extending between the two end plates. By varying the electric power applied to the piezo actuator, the axial length of the actuator can be varied, and thus the gap between the end plates varied. As alternatives to piezo-electric actuators, the tuning mechanism may employ liquid crystals, temperature, pressure, and other mechanisms. In U.S. Pat. No. 6,040,932 to Duck et al, a system and method are discussed for de-multiplexing closely spaced optical channels separated from one another by a distance xe2x80x9cdxe2x80x9d. A periodic multi-cavity Fabry-Perot etalon having a free spectral range of xe2x80x9c2dxe2x80x9d (or an integer multiple of 2d) is coupled to a circulator for launching an input beam. A first composite optical signal carrying channels 1, 3, . . . n is reflected from the input port of the etalon and a second composite optical signal carrying channels 2, 4, . . . nxe2x88x921 is transmitted through the etalon. Duck et al do not disclose how a suitable multi-cavity etalon could be constructed. Only the adjustable gap etalon of the Ip patent is cited, with no suggestion as to how multiple such adjustable etalons could be optically coupled. The piezo actuators and associated hardware would seemingly prevent optical contact of adjacent etalons. It is also a disadvantage that adjustable etalons as in Ip involve considerable assembly complexity and cost. Also, maintaining strict parallelism between the end plates can present additional difficulties.
It is an object of the present invention to provide a system for separating closely spaced channels in a wavelength band and to methods of making and using them. Additional objects and aspects of the invention and/or of certain preferred embodiments of the invention will be apparent from the following disclosure and detailed description.
This invention, in accordance with a first aspect, relates to a method and system for semi-multiplexing or semi-demultiplexing channels in a wavelength division multiplexed (WDM) signal. In certain preferred embodiments, WDM signals are further processed to fully multiplex or demultiplex the signal. It should be understood, that any use of the term multiplex or semi-multiplex in reference to an optical system disclosed here which is operative in both directions of operation, i. e., the multiplexing and the demultiplexing direction, is intended to mean both and either of these operations. As further discussed below, the optical systems disclosed here are especially advantageous for use with closely spaced WDM channels. An optical system in accordance with this aspect is operative in a wavelength band spanning a series of passbands each having a center wavelength spaced d nm from the center wavelength of adjacent passbands within the wavelength band. The system comprises a signal carrier, e.g., a fiberoptic waveguide or the like, capable of carrying the multiple passbands as individual channels in a WDM multiplexed signal. An interleaver is optically coupled to the signal carrier and comprises a plurality of optically matched and directly optically coupled etalons, having a periodic passband within the wavelength band of the system. More specifically, the interleaver has passbands of width less than d nm and a period equal to zd nm, wherein z is an integer value of at least 3. It will be understood by those skilled in the art, that the necessary degree of precision in the passband width and period of the interleaver will depend in large part on the performance requirements of the optical system. At least one of the optically coupled etalons of the interleaver comprises first and second selectively transparent thin film mirror coatings on opposite first and second surfaces, respectively, of a bulk optic. The bulk optic comprises a solid, optically transparent body, and the dimension of the light path through the bulk optic defines the cavity spacing of the etalon. Typically, the bulk optic comprises a diced portion of an optical substrate, such as a silica wafer known for use in sputtering methods for making passband filters and the like. In preferred embodiments the selectively transparent surfaces are thin film mirror coatings comprising, for example, a film stack of alternating high and low refractive index oxides or a metal thin film in accordance with known thin film technologies. The interleaver preferably is operative in the optical system to pass a first set of the individual channel passbands satisfying the equation 1+xz, wherein z is an integer value of at least 3 and x is an integer value of 0 or greater, as a semi-multiplexed signal and to reject a second set of the passbands not meeting the terms of the equation descried above. The individual channels can be isolated from the semi-demultiplexed signal by further processing such signal using, for example, a set of individual channel passband filters in accordance with known techniques. Advantageously, as disclosed above, the individual passband filters are presented with a semi-demultiplexed signal containing the desired individual channel signals, and from which the passband(s) immediately adjacent to such desired passbands have been removed by the interleaver. For this reason, an individual passband filter will be suitable and operative in the optical system, even if its passband is larger (i.e., twice the wavelength span) of the corresponding channel. As noted above, channel filters having wider passband can be less expensive to produce. The resulting system cost reduction can exceed the cost of the added interleaver. Thus, overall system cost saving can be achieved. In accordance with certain preferred embodiments, the optical system further comprises a set of passband filters mounted in a common housing with the interleaver and optically coupled to the interleaver to receive at least a portion of the semi-demultiplexed signal from an output port of the interleaver
In accordance with one aspect, an optical system operative in a wavelength band divided into multiple channels comprises a series of interleavers connected input port to input port. For example, an optical system employing a series of 1xc3x973 interleavers may employ 2 interleavers or 3 interleavers depending on whether or not the final semi-demultiplexed signal is to be passed through an interleaver to clean it. Similarly, an optical system employing 1xc3x974 interleavers may employ 3 or 4 interleavers. Further, a series of interleavers each having an input port and an output port and each operative to pass a different subset of passbands within the wavelength range received via the input port, the subset of passbands of each of the interleavers being different from the subset of passbands of the other of the interleavers, and each directly coupled to an interleaver, and each interleaver comprising a plurality of optically matched and directly optically coupled etalons, at least one of the etalons being a bulk optic etalon comprising first and second selectively transparent thin film mirror coatings on opposite surfaces of a bulk optic defining the cavity spacing of the etalon, the width of the passbands of the interleaver being substantially equal to the passband width of the channels 1 through n and the period of the interleaver being zd nm, where z is an integer value of at least 3. Interleavers, of the type described here, are capable of xe2x80x9cinterleavingxe2x80x9d channels of an optical signal. xe2x80x9cInterleavedxe2x80x9d for the purposes of this application is to comprising passbands of a first set following those passbands of another set in a generally alternating pattern, but not necessarily being immediately adjacent each other in the wavelength band and not necessarily being of the same width. A semi-demultiplexed signal according to the optical system disclosed here may comprise adjacent channels which will be further demultiplexed by other interleavers in a series of interleavers. It should be recognized that while each of the interleavers in a series of interleavers employed in a preferred embodiment of the operating system disclosed here, typically will have passbands of the same bandwidth and same period for a typical operating system employing a series of 1xc3x973 interleavers, the interleavers will each pass its own unique set of passbands, i.e., a different set of channels.
In accordance with one aspect, an optical system operative in a wavelength band divided into multiple channels comprises at least one signal carrier capable of carrying channels 1 through n. Each channel of the signal has an allocated passband portion of the wavelength band with a center wavelength spaced d nm from the center wavelength of adjacent channels within the band. The optical system also comprises at least one interleaver coupled to the signal carrier and comprising a plurality of optically matched and directly optically coupled etalons. The interleaver has a periodic passband of width d nm and a period equal to zd nm, wherein z is an integer value of at least 3. Further, at least one of the optically matched and directly optically coupled etalons of the interleaver comprises first and second selectively transparent thin film mirror coatings on opposite surfaces of a cavity formed by a bulk optic comprising a solid optically transparent body. The bulk optic defines the cavity spacing of the etalon. The interleaver formed from the etalons has an input port for receiving multiplexed signals. (As described earlier, the interleavers disclosed here typically are capable in an optical system of either multiplexing or de-multiplexing optical signals. reference to either in such cases is intended to include both multiplexing and de-multiplexing.) In accordance with certain preferred embodiments the optical system is operative in the C band, generally understood to be from about 1530 nm to about 1570 nm. According to certain preferred embodiments, the etalons forming the interleaver may further comprise a bonding layer. A bonding layer is any layer of bonding material on a surface of an etalon and used to physically attach that etalon to an adjacent etalon.
The etalons of the interleavers disclosed above are directly optically coupled, as the term is used here, when they are optically coupled, i.e., are in the same optical path, and furthermore are in optical contact or are otherwise in physical contact with each other and/or mounted to each other (e.g., by bonding material in or out of the optical path) or mounted together in the same housing or by the some fixture. An air space may be separating the etalons (or etalon stacks) or the etalons may be in direct surface-to-surface contact. Similarly, optical components of an optical filter element of the systems disclosed here, that are directly optically coupled in accordance with the present disclosure, have no intervening optical component(s) performing substantial channel filtering or like optical operations on the passed signal. In particular, any signal passed by the first optical component of the optical filter element arrives at the second optical component of the optical filter element without any intervening wavelength filtering optical operations to add or drop channels or the like.
According to certain preferred embodiments, the bulk-optic etalons may be placed in optical contact with each other, i.e., the thin film coatings of one such etalon is in direct and substantially continuous surface-to-surface contact with the thin film coatings of an adjacent etalon in the stack, or may be placed in contact using one or more bonding layers between adjacent etalons. According to certain preferred embodiments, the signal carrier is selected from the group consisting of optical fiber, waveguides, and air space. Preferably the signal carrier in the system disclosed here is optical fiber.
In accordance with certain preferred embodiments, the optical system comprises light sources operative to generate signals in some or all of the located channels of the system. Suitable light sources include, for example, single diode emitters and lasers, each preferably emitting light of a specified wavelength or within a wavelength band limited to the allocated passband of a corresponding channel of the optical system. Preferred light sources for optical systems disclosed here include lasers emitting light in the C band. It will be readily apparent to one skilled in the art, given the benefit of this disclosure, which wavelengths and light sources are suitable to meet the optical and other performance requirements of a particular optical system.
In accordance with another aspect, an optical system as disclosed above further comprises second and third interleavers. The second interleaver is optically coupled to the first interleaver, to receive a semi-demultiplexed signal reflected by (i.e., not passed through) the first interleaver. This second interleaver is downstream of the first (again, bearing in mind these systems and components are operable in both directions) and is operative to receive the set of passbands or channels rejected, i.e., not passed, by the first interleaver. This second interleaver is also operative to pass the second channel of the original channel and any channels zd nm from the second of the original channels of the semi-de-multiplexed signal reflected from the first interleaver. All other channels not meeting this requirement are reflected from the second interleaver. The third interleaver is optically coupled to the second interleaver, to receive a semi-demultiplexed signal reflected by (i.e., not passed through) the second interleaver. This third interleaver is downstream of the second (again, bearing in mind these systems and components are operable in both directions) and is operative to receive the set of passbands or channels rejected, i.e., not passed, by the second interleaver. The third interleaver is also operative to pass the third channel of the original signals and any other channels spaced zd nm from the third channel of the original channels of the semi-demultiplexed signal reflected from the second interleaver. Preferably the three interleavers are housed in a common housing or fixture. As further described elsewhere in this disclosure, the second and third interleavers are especially useful, for example, to further separate the semi-demultiplexed channels rejected from the first interleaver. For example, a first 50 GHz interleaver, that is an interleaver, which has 50 GHz spaced passbands (xcx9c0.4 nm), and a 200 GHz period, is operative to reflect 50 GHz width channels that are not spaced zd nm from the first channel. The 50 GHz interleaver of the optical system can be employed to pass a semi-demultiplexed signal comprising the first channel and any channels spaced zd nm form the first channel to a first signal carrier, such as an optical fiber. Such semi-demultiplexed signal can be further processed. Typically, e.g., the passed signal comprising the first channel and channels spaced zd nm form the fist channel can be further demultiplexed into individual channels using a set of 100 GHz passband filters. The 100 GHz individual passband filters are operative to pass the individual 50 GHz passed channels because the reflected 50 GHz channels that were in the original signal have been removed from the original signal. The channels of the reflected signal can then be further separated using a second interleaver, which has 50 GHz passbands operative to reject (i.e., reflect) the 50 GHz width channels that are not spaced zd nm from the second channel. The second 50 GHz interleaver of the optical system can be employed to pass a semi-demultiplexed signal comprising the second channel and any channels spaced zd nm form the second channel to a second signal carrier, such as an optical fiber. Such semi-demultiplexed signal can be further processed. Typically, e.g., the passed signal comprising the second channel and channels spaced zd nm form the second channel can be further demultiplexed into individual channels using a set of 100 GHz passband filters. The 100 GHz individual passband filters are operative to pass the individual 50 GHz passed channels because the reflected 50 GHz channels that were in the original signal have been removed from the semi-demultiplexed signal. The channels of the reflected signal, the second semi-demultiplexed signal, can then be further separated using a third interleaver with 50 GHz passbands operative to reject the 50 GHz width channels that are not spaced zd nm from the third channel. The third 50 GHz interleaver of the optical system can be employed to pass a second semi-demultiplexed signal from the comprising the third channel and any channels spaced zd nm form the third channel to a third signal carrier, such as an optical fiber. Such second semi-demultiplexed signal can be further processed. Typically, e.g., the passed signal comprising the third channel and channels spaced zd nm from the third channel can be further de-multiplexed into individual channels using a set of 100 GHz passband filters. The 100 GHz individual passband filters are operative to pass the individual 50 GHz passed channels because the reflected 50 GHz channels that were in the second semi-demultiplexed signal have been removed from the second semi-demultiplexed signal. The channels of the reflected signal from the third interleaver can then be further separated using individual passband filters.
In accordance with certain preferred embodiments, it may be advantageous to further process the signal after the multi-channel semi-demultiplexed signal is either reflected or passed through the interleaver. Further processing steps may comprise amplification or re-filtering. It may be advantageous to re-filter the signal to remove any remaining levels of the previously filtered signal.
A further advantage of using interleavers in the fashion described above arises from the ability to gracefully expand an optical system. For example, if a system with 25 channels is desired for the first year, with 25 more channels being desired each year for three years, it is more advantageous to install a system that uses every forth channel across the C band than to install 25 channels over a forth of the C band. It is advantageous because amplifiers and other equipment function more efficiently if the entire range of the C band is in use. Additionally, in the beginning phases of installation, less precise individual channel filters can be purchased at a significant cost savings.
In accordance with another aspect, an optical system as disclosed above is operative within a wavelength band and comprises at least one port for launching optical signals from the signal carrier to the interleaver and at least one port for receiving semi-demultiplexed signals passed by the interleaver. In accordance with certain preferred embodiments of such optical systems, there is a first port, that can be referred to as a first signal carrier port, for launching multiplexed signals from the signal carrier to an input port of the interleaver, a second port, preferably a second signal carrier port, an input port to a passband array, a sensor array or detectors or the like, for receiving semi-demultiplexed signals from an output port of the interleaver, specifically, the semi-demultiplexed signals passed by the interleaver, and a third port, again preferably being a signal carrier port, an input port to a passband array, a sensor array or detectors or the like, for receiving semi-demultiplexed signals reflected back from the input port of the interleaver. Where all of the etalons of the interleaver, or at least an etalon at the end of a stack of etalons forming the interleaver, is of the bulk-optic type disclosed above, having first and second selectively transparent thin film mirror coatings on opposite surfaces of a cavity formed by a bulk optic, the input port of the interleaver preferably is one of the aforesaid opposite surfaces of such etalon. The term xe2x80x9cbulk optic etalonxe2x80x9d is used here to describe the novel optical etalons described here. Likewise, the output port of the interleaver, i.e., the opposite end of the light path through the interleaver, from which semi-demultiplexed signals passed by the interleaver are emitted, preferably is a surface of such a bulk optic etalon in the stack of etalons forming the interleaver. It will apparent to those skilled in the art, however, that the interleavers disclosed here optionally may comprise other thin films or optical elements or devices optically coupled with the stacked etalons and positioned at either end of the light path, such that the input port of the interleaver or the output port may be a surface of any of these. Thus, the first interleaver of the optical system in accordance with this aspect will pass the signal containing a set of channels that meet the equation 1xc3x97xz, wherein z is one of the values 3, 4, 5 . . . , x is one of the values 0, 1, 2, . . . (e.g. an integer value of at least 0 or greater than or equal to 0). The other semi-demultiplexed signal, i.e., the reflected signal from its input port, the signal comprises all other channels that do not meet the terms of the equation for the passed channels. As used herein, semi-demultiplexed signals comprise more than one channel, or at least the passbands corresponding to multiple channels of the optical system. At any given point in time, one or more of the channels may not be carrying data or other active signal, but the interleaver nevertheless is operative to pass that channel (or reflect it, as the case may be).
In accordance with another preferred embodiment an interleaver is described which passes a second set of signals from the second of the opposite surfaces which satisfies the equation 1xc3x97xz, wherein z is one of the values 3, 4, 5 . . . , x is one of the values 0, 1, 2, . . . The channels of the second set, reflected from the first of the opposite surfaces are all remaining channels not satisfying the above equation. Each channel in the signal from the second of the opposite surfaces must satisfy the equation. For example, a signal which comprises wavelengths xcex1, xcex2, xcex3, xcex4, xcex5, xcex6, xcex7, xcex8, and xcex9 (corresponding to channels 1, 2, 3, 4, 5, 6, 7, 8, and 9) launched at a 1xc3x974 interleaver, the interleaver will pass channels 1, 5, and 9. Channels 2, 3, 4, 6, 7, and 8 will be reflected from the first of the opposite surfaces. Channel 1 meets the equation and will be passed through the interleaver. In this example z equals 4 because it is a 1xc3x974 interleaver. When x is equal to 0 the equation equals 1, which corresponds to channel 1. Channel 5 meets the equation when x is equal to 2, and channel 9 meets the equation where x is equal to 3.
According to another aspect, the bulk optic of an etalon incorporated into the aforesaid interleaver of the optical system comprises a solid body optically transparent (at the wavelengths of interest) and, together with the transparent body in the bulk optic, a wedge correcting coating (referred to here generally as a xe2x80x9cwedge coatingxe2x80x9d) and/or a thickness-adjustment layer on at least one of the two path-of-light surfaces of the optically transparent body. The wedge coating, further described below, establishes high precision parallelism of the surfaces of the etalon carrying the selectively transparent, thin film mirror coatings of the etalon. As disclosed above, the thickness of the bulk optic, i.e., the dimension between the selectively transparent, parallel surfaces, defines the physical dimension of the cavity spacing. The physical thickness of the bulk optic is its dimension in the direction of the light path, i.e., between its coated surfaces on opposite sides of the bulk optic. (The index of refraction of the bulk optic together with the physical dimension establishes the optical path length.) In accordance with this aspect, such thickness includes the transparent body as well as any wedge coating and/or thickness-adjusting layer. Preferably, the bulk optic, including any wedge coating and/or thickness-adjusting layer, has an optical thickness equal to an integral number of half waves for the wavelengths of interest. If a wedge coating is used, the thickness of the wedge coating varies progressively across the etalon. That is, the thickness of the wedge coating, viewed in cross-section in at least one plane orthogonal to the parallel, selectively transparent surfaces of the etalon, has a thickness that increases (or decreases in the opposite direction) continuously, typically approximately linearly, to compensate for non-parallelism, or xe2x80x9cwedgexe2x80x9d, in the underlying body of the bulk optic. The bulk optic can be diced from a wafer on which a wedge coating and the two thin film coatings have been deposited by magnetron sputtering, ion beam sputtering or other known deposition techniques. Preferably, surface polishing is performed to first polish the wafer.
It is a significant advantage that the interleaver of the optical systems disclosed here can employ one or more bulk optic etalons of the type disclosed above, comprising an optically transparent body and optionally a wedge coating and/or thickness adjusting layer to define the cavity spacing of the etalon. Substantial cost savings and production simplification can be realized in accordance with at least certain preferred embodiments of the optical systems employing interleavers comprising stacked, optically matched, directly optically coupled bulk-optic etalons. Further, robust and accurate stacked, optically coupled etalons can be achieved using production techniques whose application will be readily understood by those skilled in the art given the benefit of this disclosure.
In accordance with another aspect a method of making an optical system for operating within a wavelength band comprises the steps of providing an interleaver as disclosed above, comprising a plurality of optically matched and directly optically coupled etalons, wherein at least one of the etalons comprises first and second selectively transparent thin film mirror coatings on opposite surfaces of a bulk optic defining the cavity spacing of the etalon. The interleaver is optically coupled to a source of WDM signals and is optically coupled to at least two devices to receive signals processed by the interleaver. A first device receives the signals reflected from a first surface of the interleaver. A second device receives signals passed through the interleaver.
In accordance with another aspect, additional cavities or etalons can be deposited or otherwise formed on either surfaces of a bulk optic etalon suitable for use in an interleaver. Specifically, thin film etalons can be formed on the input or output surface of such etalons, by suitable deposition techniques, such as, for example, ion beam sputtering, magnetron sputtering, or other physical vapor deposition technique. More specifically, following deposition of a suitable spacer layer overlaying the thin film stacks on either surface of the bulk optic etalon, a cavity can be deposited by, for example, sputtering a first suitable thin film coating or stack, such as a sequence of alternating H/L/H films, followed by deposition of a cavity film, followed by deposition of a second thin film H/L/H coating or stack which preferably is substantially identical to the first thin film coating. Similarly, one or more such additional thin film etalons can be deposited thereafter employing suitable half-wave spacer layers between, in accordance with thin film principles well known to those skilled in the art. Thus, the advantage of improved optical performance characteristics of a multi-cavity device can be achieved, incorporating a bulk optic etalon of the type disclosed above together with additional thin film etalons unitary therewith by depositing such thin film etalons thereon using sputtering or other suitable deposition techniques. Any suitable materials disclosed above, and other suitable materials known to those skilled in the art, may be used for the thin films of the thin film etalons including but not limited to Ta2O5, ZrO2, TiO2, Al2O5, SiO2, and MgF. The multi-cavity deposition product, described above, is suitable for use, generally together with or in place of the single cavity embodiments of the bulk optic etalons disclosed here.
In accordance with certain embodiments, the etalons forming the interleaver in an optical system operative in a wavelength band divided into multiple channels, as described above, are bonded to each other. Each etalon comprises any or all of the components listed above including, but not limited to, a bulk optic, optionally comprising a wedge coating and/or a thickness-adjustment layer, and thin film mirror coatings on the surfaces of the bulk optic. Between adjacent etalons may be a layer of bonding material that acts to optically couple the etalons together. The thickness of the bonding layer is preferably equal to an odd number of QWOTs. This bonding layer may be an adhesive, such as an epoxy, e.g. the epoxies available from Epoxy Technology, Billerica, Mass. such as, EPO-TEK 353 ND, an adhesive optionally having a monolayer of small beads embedded in the adhesive to facilitate precise spacing of the adjacent etalons, fritted glass or any other composition or material that may be deposited to an odd number of QWOTs and is capable of bonding the etalons together.
In accordance with certain preferred embodiments, adjacent etalons forming the interleaver of the optical system operative in a wavelength band divided into multiple channels are joined using a layer of epoxy or other suitable adhesive. The adhesive can be applied using any suitable technique. The adhesive may be deposited onto wafers, coupons, or onto individual etalons. Two or more wafers, two or more coupons, or individual etalons are stacked in physical contact after the adhesive is applied. After being placed in physical contact, the adhesive layer bonds the etalons forming stacked, optically coupled etalons. One skilled in the art will recognize, given the benefit of this disclosure, that this process may be repeated using additional etalons to increase the number of etalons that are coupled and stacked.
Optical systems comprising the interleaver disclosed here offer several advantages including considerable cost savings and precise optical performance characteristics. In addition to incorporation of the interleaver into new optical systems, existing optical systems may be modified, adapted or altered to incorporate the interleaver described here to provide higher signal throughput rates, for example. Those skilled in the art, given the benefit of this disclosure, will be able to incorporate the interleaver and technologies related to and based on the interleaver described here into existing optical systems.
The interleavers of the optical systems disclosed here, and the methods disclosed for their production will be recognized by those skilled in the art to represent a significant technological advance. Robust interleavers can be produced meeting precise optical performance characteristics, with advantageously low production costs and good production flexibility. In preferred embodiments, the interleavers have the advantageous attributes of small size, simple and potentially inexpensive construction, and good optical performance, including low loss, low polarization dependent loss and polarization mode dispersion, and low chromatic dispersion. Additional features and advantages will be understood from the following detailed description of certain preferred embodiments.
Additional advantages and features of the optical systems and components disclosed here will be apparent to those skilled in the art, given the benefit of the foregoing disclosure and the following detailed description of certain preferred embodiments.